1. Technical Field
The present disclosure relates generally to oil and gas wells, and more particularly to controlling gas leaking from an annular gap between surface and production casings thereof.
2. Description of the Related Art
Historically, hydrocarbon wells for producing natural gas have been drilled using a larger diameter surface casing inside which is inserted a relatively smaller production casing that extends down into the production zone where the production casing is perforated to permit the production tubing to be fluidly coupled to the hydrocarbon source and control flow to the surface. According to Oil Country Tubular Goods “OCTG” standards, the surface casing typically has a diameter of 177.8 mm or 7 inches, while the production casing typically has a diameter of 114.3 mm or 4.5 inches. Once both casings are in place, the installer “cements” the annulus that exists between an interior of the surface casing and an exterior of the production casing, so as to prevent pressurization of the casings from the escape of gas up the annulus.
The importance of the problems associated with uncontrolled gas leaks is well documented. Uncontrolled gas leaks can also result from tubing and casing leaks, poor drilling practices, improper cement selection, inadequate zonal isolation and production cycling. Modern regulation of the oil and gas industry has resulted in the need to install surface casing vents, including retroactively installing surface casing vents on older wells. Many wells experience sustained casing pressure due to from the uncontrolled migration of gas to the surface, associated with annular flow which results from a number of causes, including inadequate cementation. With the increase in the importance, and hence value, of natural gas, gas leaks have become a very significant issue. For environmental and other reasons it is therefore desirable to find an affordable and safe way to control the migration of gas to the surface even in wells that are no longer producing on a commercial scale.
Previous attempts by the gas production industry to address the problem have concentrated on variations of a one-piece solution to sealing the annular gap. In one example, well owners attempted to weld steel plates onto the surface casing stub to seal the gap to the production casing. Disadvantageously, not all of the production casings were centered in the surface casing, so the solution would not work on all wells. Such an approach also presented significant safety issues. For instance, if a welder accidentally burned a hole in the production casing, then there could be an uncontrolled escape of gas leading to injuries and/or death. Further, since some of these wells are already venting natural gas up the annulus between the casings—welding is not an option at all.
Another example was to suspend production at the well, pull the production tubing, set a bridge plug, remove the production tubing spool, install a surface casing spool with a vent, then reinstall everything else. The cost of this was typically $25,000 to $35,000 per well. Such is a prohibitively costly approach, particularly for wells that are no longer producing on a commercial scale. Accordingly it is desirable to identify a way to seal and vent well-heads, which is both safe and cost-effective.
Devices sometimes known as “mud cans” were used while pulling tubing or drill pipes still filled with fluid. The mud can would be wrapped around the joint between 2 lengths of production tubing or drill pipe and then quick-latched to hold the device in place while breaking the joint to disconnect the pipes so that the fluid could drain through a port and out to a vacuum truck. Mud cans were not built to hold pressure, they were more like a funnel for redirecting drilling fluid while disassembling a drill string. The mud cans had the same size opening at each end and were always open to the vacuum truck, but the mud cans still leaked fluid around the edges. While mud cans appear similar in structure to some embodiments of the structures disclosed in the detailed description herein, the similarities are superficial and mud cans must not be confused with such structures. Mud cans are for use in a very different application and have very different operational specifications. Basically, the so-called mud can is for a temporary, non-sealing application and is small in volume and light-gauge in construction—such that it is completely unsuitable for the current application.